The present invention relates to an improved vibratory screening machine and an improved vibratory screen and to an improved tensioning structure for a vibratory screening machine.
In the past, a conventional way of mounting vibratory screens on vibratory screening machines was by utilizing elongated channel members on the sides of the machines which interfitted with channels formed at the side edges of a screening screen. However, this system had certain deficiencies. One deficiency was that the channels formed on the side edges of the screen would distort. Another deficiency was that the tensioning channels had to be moved clear of the channels on the edges of the screens before the screens could be demounted from the machine. This was a time-consuming operation, considering that generally twelve bolts had to be loosened on each side of the machine before screens could be removed and thereafter all twenty-four bolts had to be tightened after new screens had been replaced. In addition, the use of the foregoing channel-type of tensioning structure was especially detrimental when used in conjunction with undulating screening screens because the material to be screened would accumulate in the areas of the channels and thus create turbulent flow of the material to be screened which caused excessive wear on the undulations adjacent the side edges of the screens. Additionally, the foregoing type of tensioning system utilizing channels required the bolts which moved the tensioning channels to pass through apertures in the sides of the machine above the screens. Thus, material to be screened could pass through these apertures and mix with the material which passed through the screens. In addition to the foregoing, since the channels on both sides of the machine had to be loosened in order to remove and replace the screens, both sides of the screening machine had to be placed so that access could be had thereto. In certain instances this required premium floor space, especially on offshore oil drilling rigs. It is with addressing the foregoing deficiencies of the prior art that the present invention is concerned.